title: Reduced D2-mediated signaling activity and trans-synaptic upregulation of D1 and D2 dopamine receptors in mice overexpressing the dopamine transporter.
abstract: The dopamine transporter (DAT) regulates the temporal and spatial actions of dopamine by reuptaking this neurotransmitter into the presynaptic neurons. We recently generated transgenic mice overexpressing DAT (DAT-tg) that have a 3-fold increase in DAT protein levels which results in a 40% reduction of the extracellular DA concentration in the striatum. The aim of this study was to examine the effect of this reduction in dopaminergic tone on postsynaptic responses mediated by dopamine receptors. We report here that DAT-tg mice have increased levels of striatal D1 (30%) and D2 (approximately 60%) dopamine receptors with D1 receptor signaling components not significantly altered, as evidenced by unaffected basal or stimulated levels of phospho-GluR1 (Ser845) and phospho-ERK2. However, the novel D2 mediated Akt signaling is markedly altered in DAT-tg animals. In particular, there is a 300% increase in the basal levels of phospho-Akt in the striatum of DAT-tg, reflecting the reduced extracellular dopamine tone in these animals. This increase in basal pAkt levels can be pharmacologically recapitulated by partial dopamine depletion in WT mice treated with the selective tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (alpha-MPT). Behaviorally, DAT-tg animals demonstrate an augmented synergistic interaction between up-regulated D1 and D2 receptors, which results in increased climbing behavior in transgenic mice after stimulation with either apomorphine or a co-administration of selective D1 and D2 receptor agonists. In sum, our study reveals that hypodopaminegia caused by up-regulation of DAT results in significant alterations at postsynaptic receptor function with most notable dysregulation at the level of D2 receptor signaling.
authors.affiliation: Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Valentina
authors.initials: V
authors.lastname: Ghisi
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Ramsey
authors.forename: Bernard
authors.initials: B
authors.lastname: Masri
authors.forename: Raul R
authors.initials: RR
authors.lastname: Gainetdinov
authors.forename: Marc G
authors.initials: MG
authors.lastname: Caron
authors.forename: Ali
authors.initials: A
authors.lastname: Salahpour
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D003342:Corpus Striatum / Q000378:metabolism; D018491:Dopamine Agonists / Q000494:pharmacology; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019257:Quinpirole / Q000494:pharmacology; D017447:Receptors, Dopamine D1 / Q000819:agonists / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000378:metabolism*; D015398:Signal Transduction; D015854:Up-Regulation; D019805:alpha-Methyltyrosine / Q000494:pharmacology
chemical_list: D001552:Benzazepines; D018491:Dopamine Agonists; D050483:Dopamine Plasma Membrane Transport Proteins; D004791:Enzyme Inhibitors; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D019257:Quinpirole; D019805:alpha-Methyltyrosine; C067113:SK&F 81297; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D001058:Apomorphine